The community structure of bryophytes and macrolichens in Madeira's natural forest: the effects of environmental variables and relations to old-growth forests
Ruas, Sara; Bergamini, Ariel; Carvalho, Palmira; Fontinha, Susana; Sim-Sim, Manuela
The distribution of bryophytes and lichens is influenced by topographic, geological and macroclimatic factors and by smaller-scale factors such as light and humidity. This study addresses the following questions in relation to Madeira's laurel forest: a) How does the community composition of bryophytes and macrolichens react to environmental factors? b) Do different groups have different niches? c) Which species are associated with undisturbed areas of the forest? We sampled 92 circular plots occupying an area of 100 m2 that comprised four ground subplots and two trees where bryophytes and macrolichens were inventoried. We recorded environmental variables (e.g. rock cover) in the field and extracted additional variables from GIS maps. We performed two Canonical correspondence analyses for bryophyte and lichen communities (CCA) and an Indicator species analysis (ISA) to understand which species were associated with undisturbed forest. Temperature was closely related to the first ordination axes and was the most important environmental variable for both communities. Since temperature is strongly correlated to altitude, this gradient is best seen as a complex altitudinal gradient. The second important gradient structuring both bryophytes and macrolichen communities was human intervention (considered as detectable forest alteration by human activities). The results of mean comparisons between groups indicate that significant differences exist only between liverworts and mosses. Liverworts are linked to more humid and sheltered areas of the forest. Among the species obtained by the ISA, four are endemic bryophytes and four are macrolichens belonging to the 'New Index of Ecological Continuity'. Past and present human activities influence the community structure of both groups. Therefore, to assess the success of conservation measures, we suggest establishing a system based on monitoring indicator species.